It is known that the formation can be improved by causing high-frequency small-scale vibration in the fiber suspension on a forming fabric by means of a roll having longitudinal grooves, disposed under the forming fabric, whereby dispersion of fiber flocs is brought about.
In turbulence rolls having a grooved surface such as those described in the German patent application 1611761, the fabric on the roll will move towards the roll center every time a groove passes under the fabric. The displacement of the wire and the frequency of the oscillations caused by the roll depend on the gap of the grooves, the roll diameter and the rotational speed of the roll. The oscillation of the wire keeps the partially formed mat fluidized so that it dewaters more readily, redisperses the stock forming into flocs and prevents sealing of the fabric. It also causes dewatering to a certain degree by means of the repeated pumping action of the fabric against the stock and the mat.
In web formers using dilute stock in which large amounts of water have to be removed through the forming fabric, the flow resistance of the drainage and supporting means should be low. This means that normally rolls cannot be used immediately after the headbox. At high speeds, the land area between the grooves produces pressure pulses detrimental to the sheet quality. Therefore, static elements such as foils must be used. In certain applications, however, for instance in web formers having a curved drainage zone, static elements cause considerable frictional forces and increase the tension of the wire wherefor a rotating roll would be preferred.
The object of the present invention is to provide an improved turbulence roll which can be used in various types of web formers and which is particularly well adapted to be used in a multilayer filter paper machine having an inclined wire portion the inclination of which is gradually decreasing.
Other objects, features and advantages of the invention will be readily apparent from the following description of a representative embodiment thereof, taken in conjunction with the accompanying drawing although variations and modifications may be effected without departing from the spirit and scope of the novel concept embodied in the following detailed description of the invention.